This invention relates to the upgrading of coal liquids hydrogenation and more particularly to a method for improving the activity of the catalyst used in the upgrading of coal liquids.
The upgrading of coal liquids consists of (1) hydrocracking of large molecules and (2) heteroatoms removal. In order to crack the large and complex molecules, these molecules have to be hydrogenated before they are cracked. Thus, to hydrocrack these large molecules, a good hydrogenation catalyst is essential. A good hydrogenation catalyst will serve the purpose of both the hydrogenation of the large molecules and removal of heteroatoms.
In the upgrading of coal liquids, the catalyst which is used, e.g., in an ebullated bed reactor, is generally presulfided before making contact with a coal liquid feed. This is essential in that the catalyst should be in a sulfided state in order to obtain maximum hydrogenation activity in the upgrading process. However, in the treatment of a coal liquid, the catalyst as it ages loses some of the sulfur and does not have a sufficient amount of sulfur to remain in the desired sulfided state. During the coal liquid upgrading process, the sulfur which has been placed on the catalyst during presulfiding, is removed by ammonia which evolves from the coal liquid feed.
Moreover, in coal liquid upgrading by hydrotreating, the sulfiding of the hydrotreating catalyst from feed sulfur and H.sub.2 S in the reactor system is often not enough to maintain its activity because of (a) a low concentration of sulfur in the feed, and (b) a high nitrogen content of feed which results in a high ammonia yield which in turn consummes H.sub.2 S to form sulfide compounds of ammonia.
The presulfiding of the catalyst will maintain the activity of the catalyst initially but unless there is an adequate amount of sulfur concentration maintained in the catalyst, the activity of the catalyst will diminish. Therefore, there is a need to provide additional sulfur in the reaction process so that the catalyst will be maintained in a sulfided state, i.e., an active state for hydrogenation.
According to the present invention as described below, the catalyst activity can be maintained by adding a non-corrosive compound such as a mercaptan along with the coal liquid feed.